A very common case study for volcanoes is the eruption of Mount St Helens in the USA in 1980. Other case studies include Mount Etna in Sicily and Heimaey in Iceland in 1973.
Mount St Helens in Washington State began its most recent series of eruptions in 1980 when a massive landslide and powerful explosive eruption created a large crater, and ended six years later after more than a dozen eruptions of lava built a dome in the crater.
The first sign of activity began in the spring of 1980 with a series of small earthquakes. After thousands of additional earthquakes and steam explosions, a cataclysmic eruption occurred on 18 May 1980.
Mount St Helens lies close to a destructive plate boundary where the smaller Juan de Fuca plate was forced into the mantle by the larger North American plate. Friction and heat cause the plate to melt and, as it melts, molten rocks are formed. The molten rock built up until it had the chance to reach the surface through cracks in the earth’s crust.
Volcanoes are difficult to predict but, although they were unable to give a precise date, scientists tried to predict the eruption of Mount St Helens by measuring the frequency of earthquakes on the mountain.
The greater the frequency, the nearer the eruption and measuring the size of the volcanic cone shows the build-up of magma in the vent.
Scientists can also check for gas emissions (sulfur dioxide) and increased thermal activity at the crater. However, even before the eruption of Mount St Helens, scientists thought that it might still be a few weeks away.
The authorities were able to evacuate people from the areas surrounding Mount St Helens, after they identified the areas affected by the previous eruption and they set up an exclusion zone around the volcano. Emergency services were also on hand to rescue those people needing help.